Preparation of chlorosilanes from disiloxanes

ABSTRACT

Chlorosilanes are obtained by reacting disiloxanes of formula: WHEREIN R1 is hydrogen or an aliphatic or cycloalyphatic radical and X and Y are hydrogen, chlorine or WHEREIN R2 and R3 are hydrogen, chlorine or an aliphatic, cycloaliphatic, phenyl, phenylalkyl, alkylphenyl, alkoxy or cycloalkoxy radical; with thionyl chloride in the presence of sulphuric, orthophosphoric or pyrophosphoric acid.

United States Patent Lefort Sept. 5, 1972 [54] PREPARATION OFCHLOROSILANES FROM DISILOXANES [30] Foreign Application Priority DataAug. 21, 1970 France ..7030754 [52] US. Cl. ..260/448.2 E

[51] Int. Cl. ..C07f 7/12 [58] Field of Search ..260/448.2 E

[ 56] References Cited UNITED STATES PATENTS 12/1966 Findlay etal....260/448.2 E X 8/ 1968 Baronnier et al....260/448.2 E X 11/1968Lefort et a] ..260/448.2 E X OTHER PUBLICATIONS Noll, Chemistry andTechnology of Silicones, 2nd Ed., Academic Press, NY. (1968), pps. 233-234.

Primary Examiner-Delbert E. Gantz Assistant ExaminerP. F. Shaver [5 7]ABSTRACT Chlorosilanes are obtained by reacting disiloxanes of formula:

wherein R is hydrogen or an aliphatic or cycloalyphatic radical and Xand Y are hydrogen, chlorine wherein R and R are hydrogen, chlorine oran aliphatic, cycloaliphatic, phenyl, phenylalkyl, alkylphenyl, alkoxyor cycloalkoxy radical; with thionyl chloride in the presence ofsulphuric, orthophosphoric or pyrophosphoric acid.

6 Claims, N0 Drawings PREPARATION OF CHLOROSILANES FROM DISILOXANES Thepresent invention relates to a process for preparing chlorosilanes byreaction of thionyl chloride with a disiloxane in the presence of astrong inorganic acid.

It is known that in general, reaction of thionyl chloride with adisiloxane allows two chlorosilanes to be obtained through breakage ofthe siloxane bond, but the presence of a catalyst is always necessary inpractice to trigger the reaction. Various catalyst systems have beenrecommended. US. Pat. No. 2,500,761, describes the use of small amountsof hydrogen halide acids or metal halides. Acetic acid has also beenused tov catalyse the cleavage of the siloxane bond (J. Prakt. Chem. 23,206 1964). However, these catalyst do not always make it possible tocleave the siloxane bond of all disiloxanes to give a chlorosilane.

The present invention provides a process for the preparation of achlorosilane wherein thionyl chloride is reacted, in the presence ofsulphuric acid, orthophosphoric acid or pyrophosphoric acid with adisiloxane of the general formula:

wherein the symbols Rf, which may be identical or different, eachrepresent a hydrogen atom, or a straight or branched, saturated orunsaturated, aliphatic hydrocarbon radical having up to six carbonatoms, or a saturated or unsaturated cycloaliphatie hydrocarbon radicalhaving five or six carbon atoms in the ring; the symbols X and Y, whichmay be identical or different, each represent a hydrogen atom, achlorine atom or a silyl radical of formula:

in which the symbols R, and R;,, which may be identical or different,each represent a chlorine atom, a hydrogen atom, a straight or branched,saturated or unsaturated, aliphatic hydrocarbon radical having up to sixcarbon atoms, a saturated or unsaturated cycloaliphatic hydrocarbonradical having five or six carbon atoms in the ring, a phenyl, or aphenylalkyl or alkylphenyl radical having up to six carbon atoms in thealkyl residue, an alkoxy radical having up to six carbon atoms, or acycloalkoxy radical having five or six carbon atoms in the ring.

In the reaction, cleavage occurs at the SiO-Si bonds and, whereappropriate, also at the SiO-C bonds, in accordance with the followingequations:

Thus, depending on the chosen starting product, either a singlechlorosilane, or two different chlorosilanes, or a chlorosilane and achlorinated hydrocarbon, will be produced.

Si-O-C bonds will be broken if the symbols R, and R represent alkoxy orcycloalkoxy radicals.

Disiloxanes which may be used in the process include,tetrahydrogeno-l,3-dimethyldisiloxane, hexamethyldisiloxane,1-3-di-(chloromethyl)-tetramethyldisiloxane, l,3-di-( chloromethyl)-l,3-dimethyl-l ,3- divinyl-disiloxane, chloromethylpentamethyldisiloxane,2,2,4,4,6,6-hexamethyl-7-chloro-2,4,6-trisila-3- oxa-heptane,2,2,4,4,6-pentamethyl-6-butoxy-7- chloro-3-oxa-2,4,6-trisila-heptane,4,4,6,6- tetramethyl-1-chloro-2,2-dibutoxy-5-oxa-2,4,6-trisilaheptane,4,4,6,6-tetramethyll ,2,2-trichloro-5-oxa- 2,4,6-trisila-heptane,2,2,4,4,6,6,8,8-octamethyl-l,9- dichloro-S-oxa-2,4,6,8-tetrasila-nonane,2,4,4,6,6,8- hexamethyl-l,2,8,9-tetrachloro-5-oxa-2,4,6,8-tetrasilanonane and4,4,6,6-tetramethyll ,9-dichloro-2,2,8 ,8-tetrabutoxy-5-oxa-2,4,6,8-tetrasila-nonane.

' The quantity of the strong inorganic acid used as catalyst can vary toa great extent but an amount which is from 0.1 to 5 percent of the totalweight of the re agents is usually most suitable.

The process of the invention may be carried out by heating the reagentsusually to a temperature of to 150 C. The respective proportions of thevarious reagents are not critical but in general an amount of thionylchloride is used which is one to two times the theoretically requiredamount, (the theoretical amount being one molecule of thionyl chlorideper atom of oxygen bonded to at least one silicon atom). The process canbe carried out in the presence of a solvent and any hydrocarbon ofaliphatic, cycloaliphatic or aromatic nature can be used for thispurpose.

During the reaction, sulphur dioxide is evolved and is removed from thereaction medium at the rate at which it is formed. When the reaction hasended, the chlorosilanes produced can be recovered by any known means,for example by distillation.

The process according to the invention constitutes one stage in thepurification of monochlorosilanes. It is sometimes very difficult toobtain monochlorosilanes in the pure state from mixtures of otherchlorosilanes by usual means, such as distillation. The conversion of amonochlorosilane into its disiloxane derivative, the isolation of thisdisiloxane in the pure state and the conversion of this disiloxane backto a chlorosilane serve in accordance with this invention to regeneratethe initial chlorosilane and make it possible to obtain pure products.Furthermore, chlorosilanes with 'chloromethyl groups are valuablesynthetic reagents which are used industrially to obtainsilacycloalkanes. The Examples which follow illustrate the invention.

EXAMPLE 1 231 g of tetramethyl-l,3-dichloromethyl-disiloxane and 143 gof thionyl chloride are heated in a reaction flask, under reflux at -110C and 10 cm of sulphuric acid are run in dropwise over the entireduration of the operation. The evolution of sulphur dioxide gas endsafter 19 hours 20 minutes. Distillation yields g ofdimethylchloromethylchlorosilane, of boiling point 158 113 C as well as76 g of unconverted tetramethyldichloromethylsiloxane.

EXAMPLE 2 The procedure described in Example 1 is repeated, replacingthe 10 cm of sulphuric acid with 20 cm of phosphoric acid. The evolutionof sulphur dioxide gas ends after 21 hours 30 minutes of heating.Distillation yields 106 g of dimethylchloromethylchlorosilane of boilingpoint ,1 13 C.

By way of comparison, the procedure described above was repeatedreplacing the phosphoric acid by various other catalysts previously usedfor breaking disiloxanes:

When 2 g of anhydrous zinc chloride was used only 2 g ofdimethylchloromethylchlorosilane was obtained.

When 2 g of anhydrous aluminum chloride or 10 ml of acetic acid wereused, the reaction did not even start (there was no evolution of sulphurdioxide).

When hydrochloric acid was bubbled in at the rate of 4.5 l/hour, thetetramethyldichloromethylsiloxane did not react at all and was recoveredby distillation at the end of the experiment. 7

EXAMPLE 3 8761 g of 2,2,4,4,6,6-hexamethyl-7-chloro-2,4,6- trisila-3-oxa-heptane and 5831 g of thionyl chloride are heated in a reactionflask under reflux at 94-98 C, and 18 cm of concentrated sulphuric acidare run in over the entire duration of the operation. The evolution ofsulphur dioxide gas ceases after 15 hours heating, while 3040 g oftrimethylchlorosilane distill and are collected in. traps. The contentsremaining in the flask are thereafter rectified under reduced pressure,and 6530 g of 2,4,4-trimethyl-2,5-dichloro-2,4-disila-pentane isobtained, b.p. 94-98 C.

EXAMPLE 4 5 ll g of 2,2,4,4,6-pentamethyl-6-butoxy-7-chloro-3-oxa-2,4,6-trisila-heptane and 775 g of thionyl chloride are heated in areaction flask under reflux at ll 10 C, and 30 cm of sulphuric acid arerun in over the entire duration of the operation. After 23 hours 50minutes heating, evolution of sulphur dioxide ceases and 382 g of amixture of trimethylchlorosilane, butyl chloride and excess thionylchloride have been distilled during the operation. The contentsremaining in the flask are then rectified under reduced pressure and 287g of 2,4-dimethyl-2,4,5-trichloro-2,4-disila-pentane is obtained, imp.4040.5 C.

EXAMPLE 789 g of 4,4,6,6-tetramethyl-l-chloro-2,2-dibutoxy-5-oxa-2,4,6-trisila-heptane and 1071 g of thionyl chloride are heated ina reaction flask under reflux at 85-95 C, and 20 cm of sulphuric acidare run in over the entire duration of the operation. Evolution ofsulphur dioxide ceases after 18 hours heating. During this period, 242 gof a mixture of trimethylchlorosilane, butyl chloride and excess thionylchloride distilled. The contents remaining in the reaction flask arethen rectified under reduced pressure and pure Z-methyl-2,4,4,5-tetrachloro-2,4-disila-pentane b.p. 94.4-96.4 C.

I claim:

1. A process for the preparation of chlorosilane wherein thionylchloride is reacted, in the presence of sulphuric acid, orthophosphoricacid or pyrophosphoric acid with a disiloxane of the general formula:

is obtained,

in which the symbols R and R which may be identical or diflerent, eachrepresent a chlorine atom, a hydrogen atom, a straight orbranched,'saturated or unsaturated, aliphatic hydrocarbon radical havingup to six carbon atoms, a saturated or unsaturated cycloaliphatichydrocarbon radical having five or six carbon atoms in the ring, aphenyl, or a phenylalkyl or alkylphenyl radical having up to six carbonatoms in the alkyl residue, an alkoxy radical having up to six carbonatoms, or a cycloalkoxy radical having five or six carbon atoms in thering.

2. A process according to claim 1, wherein the quan tity of sulphuric,orthophosphoric or pyrophospheric acid used is 0.1-5 percent by weightbased on the total weight of the reagents.

3. A process according to claim 1, wherein the reaction is carried outat a temperature of -l 50 C.

4. A process according to claim 1, wherein the amount of thionylchloride used is 1-2 moles per gram atom of oxygen in the disiloxanebonded to silicon.

5. A process according to claim 1, wherein the reaction is carried outin the presence of a hydrocarbon solvent.

6. A process according to claim 1, wherein the disiloxane and thionylchloride are heated under reflux and the sulphuric, orthophosphoric orpyrophosphoric acid is run in to refluxing mixture dropwise untilevolution of sulphur dioxide ceases.

2. A process according to claim 1, wherein the quantity of sulphuric,orthophosphoric or pyrophospheric acid used is 0.1-5 percent by weightbased on the total weight of the reagents.
 3. A process according toclaim 1, wherein the reaction is carried out at a temperature of70*-150* C.
 4. A process according to claim 1, wherein the amount ofthionyl chloride used is 1-2 moles per gram atom of oxygen in thedisiloxane bonded to silicon.
 5. A process according to claim 1, whereinthe reaction is carried out in the presence of a hydrocarbon solvent. 6.A process according to claim 1, wherein the disiloxane and thionylchloride are heated under reflux and the sulphuric, orthophosphoric orpyrophosphoric acid is run in to refluxing mixture dropwise untilevolution of sulphur dioxide ceases.